1. Field of the Invention
The present invention relates to power supplies, and more particularly, to regulators for power supplies.
2. Discussion of the Background of the Invention
Many applications require power to be supplied at a particular voltage or current level. One type of power supply circuit converts the power which is available to power at the desired voltage (or current) level. However, the power input into the power supply is often unregulated so that the voltage or current of the input power may vary. Also, the load conditions on the power supply may also vary. Both of these conditions can affect the output voltage (or current) of the power supply.
To maintain the output of the power supply at a predefined level, many such power supplies have a regulator which monitors the output of the power supply and modifies the input of power to the supply as necessary. However, for switched-mode power supplies having a transformer, it is often necessary to maintain isolation between the input and output circuits of the transformer, which has complicated the design of the power supply regulators. In these power supplies, power is input into the primary coil of the transformer through a transistor switch. The output of the power supply from the secondary coil of the transformer is monitored and this information is fed back to control the transistor switch on the primary coil side of the transformer. In order to maintain isolation between the primary and secondary coils, an opto-isolator has been used to transmit the feedback information from the secondary coil side of the transformer to the switch on the primary coil side. However, these opto-isolators often have poor linearity, particularly with variations in temperature.
Another approach has been to amplitude modulate a high frequency carrier signal with the desired feedback information to couple this composite signal through a transformer. An example of such a modulator circuit is the Unitrode integrated circuit (UC 1901). However, this latter approach has often required in addition to a complex integrated circuit, several components to demodulate the amplitude modulated carrier signal.